The present invention relates to a inkjet apparatus for printing images, more particularly to such apparatus that coats the images with a durable material.
Durability is a performance criterion that is expected by consumers of photographic and other prints. This criterion includes resistance to tearing, fading, water and chemical exposure plus numerous other factors. In the current state of the art, silver halide prints demonstrate a high degree of overall durability in relation to inkjet. This fact is one of the reasons why inkjet near photographic quality printing technologies are not completely supplanting the silver halide share of the market. However, these other technologies are rapidly improving durability through the addition of materials and processes.
One example of a non-silver halide printing process that produces a durable photographic quality print is the Kodak Picture Maker. The Kodak Picture Maker creates durable prints by using the same thermal dye diffusion printing process that is used to produce the image on the media. Specifically, this printing process is one in which dye is transferred from a donor ribbon to media by means of heating a thermal print head while the print head, donor ribbon and media are in mechanical contact. By performing this process in a serial fashion for three separate primary color patches (sometimes there is a fourth black patch) in a controlled manner, an image can be produced on the media. To ensure durability, this printing process is performed one more time except that instead of dye transfer, a continuous clear overcoat material is transferred to the media. This process is often referred to as peel-apart or thermal transfer overcoat (TTO).
A second example of a non-silver halide printing process that produces a durable photographic quality print is the Canon Hyperphoto. Patents associated with this type of process are U.S. Pat. Nos. 4,832,984 and 4,785,313, as well as European Patents 0 858 905 A1 and 0 858 906 A1. In the Canon Hyperphoto, the original media has already been pre-coated with a special chemical layer prior to printing (actually done during the production of the media). This coating is designed such that during the inkjet printing process, the inks can penetrate the layer and stabilize on an ink-receiving layer below the special coating. The Canon Hyperphoto then uses a heated fuser to seal this top coating over the image after the print cycle is complete. This process is often referred to as incorporated since the durability material is already incorporated into the media prior to printing.
Recently, inkjet printing has become a popular method for printing photographic quality images. Inkjet printing is now being developed for retail photofinishing. While the printed images are of high quality, inkjet prints suffer from a number of disadvantages relative to other hard copy out puts. In particular inkjet prints have poor water fastness, light fastness, finger print resistance, and abrasion resistance. Thus there is a need for improved dye chemistry and improved overcoats. Further more, in order to increase inkjet printing through put a fast-drying receiver is required. Fast drying receivers are porous and are low gloss. Thus, an overcoat is also useful increasing the gloss of the printed image.
Overcoats could potentially provide a low cost solution because the desired protection may be packed into one layer. Hydrophobic polymers may be used to eliminate water penetration. The polymers may also be formulated to reduce the permeation of gas such as ozone that are known to bleach dyes. The overcoat may also be packed with UV screening agents to improve light fastness. Adhesion promoters such as copolymers and wetting agents may be formulated into the over coat to provide defect-free coatings that will not blister or delaminate. These ideas are being incorporated in current overcoat formulations with some success but they suffer from cost, waste, and difficulties in providing adequate protection while balancing environmental concerns at the point of use.
A polymer formulation to be coated at the point of use after a print is generated requires a solvent that meets a higher environmental standard. Solvents that are odorous, flammable and hazardous will not be acceptable. Hydrophobic polymers that provide the best protection against water damage are incompatible with a water solvent. Compromises of using hydrophilic-hydrophobic copolymers would not be effective because they are not as effective against fingerprints and abrasion. Hydrophobic lattices dispersed in water could potentially be useful but coated films are prone to pinhole defects that allow water to penetrate. They also require considerable annealing to allow the lattices to coalesce and form a continuous film. This may require extra equipment such as heaters or fusing rollers, which adds to cost and detracts from high productivity.
Even if water were to be used as the solvent, considerable cost would be associated with the removal of the water solvent. This requires a drying station, which adds to cost and productivity. When receivers are loaded with water, the receiver tends to cockle after drying. Therefore, some cost savings in the receiver design may be realized if the overcoat does not increase solvent burden on the receiver.
Supercritical carbondioxide has been studied as alternative solvent for organic materials such as high molecular weight polymers, hydrophobic polymers, surfactant copolymers, and drugs. It has been suggested as an environmentally friendly solvent.
It is a feature of the present invention that supercritical carbondioxide be used as solvent in providing overcoats for protecting inkjet prints. The advantages of using supercritical carbondioxide include the following:
1. The range of polymers can be used is be greater than if water were the solvent because supercritical carbondioxide is a better solvent than water. For example, the permissible polymers include high molecular weight hydrophobic materials. In particular, polymeric components include vinyl, acrylic, styrenic, siloxane, urethane monomers and interpolymers of the base vinyl, acrylic and styrenic, siloxane and urethane monomers; poly(methylmethacrylate), organo-silane, cellulosic esters, polyesters, and fluorinated polymers may potentially be used with a supercritical carbondioxide solvent.
2. Supercritical carbondioxide is environmentally friendly.
3. Using supercritical carbondioxide as solvents eliminates the need of a drying station because supercritical carbondioxide rapidly converts to a gas. The risk of receiver cockle is reduced or eliminated.
4. Supercritical carbondioxide dries rapidly improving productivity.
The above and other objects, advantages and novel features of the present invention will become more apparent from the accompanying detailed description thereof when considered in conjunction with the following drawings.